Oxygen therapy has been traditionally administered utilizing apparatus which provides a continuous flow of oxygen to the patient. The continuous flow technique wastes a great deal of oxygen due to the fact that inspiration, or inhalation, occurs only during approximately one third of the breathing cycle. The oxygen which continues to flow during the expiration portion of the breathing cycle is simply expelled into the atmosphere. It is therefore desireable to provide means for supplying a flow of oxygen to the patient only during the inspiration portion of the cycle.
Intermittent flow for oxygen therapy has been shown by Auerbach et al. (D. Auerbach et al., A New Oxygen Cannula System Using Intermittent Demand Nasal Flow, CHEST, 74, July 1, 1978, pages 39-44) to be an effective way of conserving oxygen and reducing its cost to the patient. By using a prototype of an intermittent demand flow device, described in the above cited article, Auerbach et al. projected a possible savings of $744.60 per year per patient at a flow rate of two liters per minute. For thousands of users at home alone, this represents a savings of millions of dollars anually. Additional significant savings could be realized for in-patient care at hospitals.
To follow the patients respiratory cycle, the intermittent demand device must be able to sense very small negative and positive pressures in or near the nostrils via a nasal cannula or a face mask. The Auerbach et al device utilizes a spring loaded diaphragm to sense these pressures. Because the diaphragm is necessarily very sensitive to extremely low pressures (.+-.0.2 millimeters Hg) it is by necessity very delicate, requiring extremely fine balancing. Such a diaphragm is extremely sensitive to external forces, such as vibration. The Auerbach et al device is reported to operate without failure for over 150 hours, too short a time for the intended usage.
It is an object of this invention to provide an intermittent demand device suitable for use in oxygen therapy which is highly dependable for greatly extended periods of time.
It is an object of this invention to provide such a device which is, in addition to being dependable, extremely sensitive to the patients respiratory cycle.
It is yet another object of this invention to provide an intermittent flow device which operates quietly and without any disturbing noise.
It is still another object of this invention to provide an intermittent flow device for oxygen therapy which consumes less oxygen than the known intermittent flow device of the prior art.